/*
 * Copyright 2002-2013 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.theme;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.servlet.ThemeResolver;
import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;
import org.springframework.web.servlet.support.RequestContextUtils;

/**
 * Interceptor that allows for changing the current theme on every request,
 * via a configurable request parameter (default parameter name: "theme").
 *
 * @author Juergen Hoeller
 * @see org.springframework.web.servlet.ThemeResolver
 * @since 20.06.2003
 */
public class ThemeChangeInterceptor extends HandlerInterceptorAdapter {

    /**
     * Default name of the theme specification parameter: "theme".
     */
    public static final String DEFAULT_PARAM_NAME = "theme";

    private String paramName = DEFAULT_PARAM_NAME;


    /**
     * Set the name of the parameter that contains a theme specification
     * in a theme change request. Default is "theme".
     */
    public void setParamName(String paramName) {
        this.paramName = paramName;
    }

    /**
     * Return the name of the parameter that contains a theme specification
     * in a theme change request.
     */
    public String getParamName() {
        return this.paramName;
    }


    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws ServletException {

        String newTheme = request.getParameter(this.paramName);
        if (newTheme != null) {
            ThemeResolver themeResolver = RequestContextUtils.getThemeResolver(request);
            if (themeResolver == null) {
                throw new IllegalStateException("No ThemeResolver found: not in a DispatcherServlet request?");
            }
            themeResolver.setThemeName(request, response, newTheme);
        }
        // Proceed in any case.
        return true;
    }

}
